Re: [Nasm-users] How to call MessageBoxA from Nasm program?

[Frank K. <fbk...@zy...>]

oh...@co... wrote:
> Hi,
> 
> I'm trying to add a call to MessageBoxA in a Nasm app.  I know how to setup the parameters for the call, but I can't get Nasm to assemble successfully.
> 
> I have added an "extern MessageBoxA" and "import MessageBoxA user32.dll" (this is on Windows), but when I do that, I get an error from parser saying that an instruction is expected.
> 
> If I comment out the "import" line, I get a linker error.
> 
> Am I not suppose to use both the "extern" and "import" lines, before the .Code line?

Mmmm, yes, but only in "-f obj" output format (which defaults to 16-bit 
and requires some "cruft" to tell Nasm we want 32-bit). Supposedly, in 
"-f win32" format, we "don't need" it. I think the reason we "don't 
need" it is that we are expected to link with an "import library" on the 
linker command line. I am told that we can create our own import library 
by assembling "extern MessageBoxA" and "import MessageBoxA user32.dll" 
(with other extern/imports we need, presumably) as "-f obj" and linking 
the produced .obj with the .obj containing your code (assembled as "-f 
win32") - despite the different linkable object formats, this is 
supposed to work. I was told this after I'd quit running Windows, so 
never had a chance to try it. I think the more "usual" way would be to 
link against an import library supplied with your linker(?). This raises 
the obvious question: which linker are you using? And what, if anything, 
came with it? I don't know much about Windows linkers - I used Alink, 
mostly, for the few Windows programs I tried. I think Golink and Polink 
are more common these days.

You might want to download the "nasmx" package:

http://www.asmcommunity.net/projects/nasmx/

Recent versions have been in .exe format, so I can't even look at it to 
see what's there. Uses Golink, it says that on the web page... If it 
doesn't include a "win32.lib" or such, the examples may give you an idea 
how to function without it.

If all else fails...

http://home.comcast.net/~fbkotler/win32nasmbase.zip

...as I recall, that includes a library that worked with "-f win32", 
although it is extremely old and obsolete...

This question about "import" comes up fairly often, and I don't really 
have a "good" answer to it, besides "it's for -f obj only" and we "don't 
need" it for -f win32... Anyone got a clearer idea on this?

Best,
Frank